Page:The Music of the Spheres.djvu/312

 all; in fact, the moon lies so close to us that it not only rolls through the shadow of the earth, but we may also see the various features, and even the shadows of those features, upon its surface.

The moon and the earth form a little system of their own and are bound together by a strong attraction. This strong attraction, called the force of gravity, has resulted in a strange thing happening to both the earth and the moon, for the earth pulls so hard on the moon that it has long since destroyed the moon's axial rotation with reference to itself, and the moon pulls so hard on the earth that it moves the great fluid body of the ocean. Thus the moon has always the same face toward the earth for it cannot turn around and show us the other side, while the pulling of the earth by the moon causes the ocean's waters to rise and fall every 12 hours and 26 minutes, or twice a day. When the Greek and Roman travelers first ventured to the ocean, they could not understand why great stretches of beaches were left dry, and with equal regularity covered up; where did the water go, and why? It seemed a hopeless mystery to people who had lived around a landlocked sea where the tide, with few exceptions, rises but a few inches. When the sun and moon are in line with the earth they co-operate in their pulling and hauling at the sea. The moon is then either "new" or "full" and it is then that the highest tides occur.